Neuroanatomy, Suboccipital Nerve
- Article Author:
- Steven Graefe
- Article Editor:
- Prasanna Tadi
- Updated:
- 11/8/2020 6:44:27 AM
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- Neuroanatomy, Suboccipital Nerve CME
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- Neuroanatomy, Suboccipital Nerve
Introduction
The suboccipital nerve, also known as the dorsal ramus of the first cervical nerve, arises from the posterior ramus of the C1 nerve. The primary function of the suboccipital nerve is the innervation of the suboccipital muscles. These muscles include the rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis superior, obliquus capitis inferior, and the semispinalis capitis. The suboccipital nerve emerges from the central canal of the spinal cord and travels inferiorly between the occipital bone and superiorly to the posterior arch of the C1 (atlas) vertebrae. Throughout the path, the suboccipital nerve travels closely with the vertebral artery. Hence, if the vertebral artery were to incur injury near the suboccipital triangle, the suboccipital nerve may likely be damaged as well. The ultimate destination of this nerve is to the suboccipital area of the posterior neck, where it branches to innervate the suboccipital muscles. These muscles are involved in postural control of the head, mainly functioning in head extension and rotation. Occasionally, the suboccipital nerve gives off a cutaneous branch that connects to either the greater or lesser occipital nerves, and this anatomical variation may play a role in occipital neuralgia and cervicogenic headaches.[1][2]
Structure and Function
At the level of C1, ventral and dorsal C1 rootlets branch off the spinal cord and connect within the subarachnoid space. The C1 rootlets, compared to the other cervical nerve rootlets, are unique in that the ventral rootlets of C1 are larger than the dorsal rootlets, and occasionally the dorsal rootlets can be absent entirely. Once these rootlets join, they exit the dura mater and divide into the ventral and dorsal rami.[1] The dorsal rami, now known as the suboccipital nerve, courses superiorly to the posterior arch of C1 and inferiorly to the vertebral artery.[3] It enters the suboccipital area by passing through the posterior atlantooccipital membrane. As it enters the suboccipital triangle, it divides into several branches to provide innervation to the muscles within this triangle and other suboccipital muscles. The suboccipital triangle is located on the posterior portion of the cervical neck, deep to the trapezius, splenius capitis, and semispinalis capitis muscles. The suboccipital triangle consists of the rectus capitis posterior major as its superomedial border, the obliquus capitis inferior muscle as its inferolateral border, and the obliquus capitis superior as its superolateral border.[2] The roof of the suboccipital triangle is the semispinalis capitis muscle, and the floor consists of the posterior arch of the C1 vertebrae and the posterior atlantooccipital membrane. Coursing through the middle of the suboccipital triangle are the suboccipital nerve and the vertebral artery. In addition to innervating the muscles of the triangle, the suboccipital nerve also innervates the semispinalis muscle and the rectus capitis posterior minor muscle. Collectively, the suboccipital muscles function as postural muscles of the head, assisting with head extension and rotation. The suboccipital muscles act by rotating the head by rotating the C1 vertebrae, the atlas, on the C2 vertebrae, the axis.[1][3][4][2][5][6]
Embryology
The suboccipital nerve forms from the interactions between the paraxial mesoderm and the visceral mesoderm at a zone called the head-neck interface (HNI), which is responsible for the development of cranial nerves X, XI, XII, and the cervical nerves C1 to C6. According to embryological studies, C1 develops primarily from somitomeres that undergo segmentation and resegmentation during embryologic development. Derangements during embryologic development likely contribute to the anatomical variations seen in the suboccipital nerve.[2][7][8]
Muscles
The suboccipital nerve innervates the following suboccipital muscles:
- The rectus capitis posterior minor muscle
- The rectus capitis posterior major muscle (the superomedial border of the suboccipital triangle)
- The obliquus capitis superior (the superolateral border of the suboccipital triangle)
- The obliquus capitis inferior muscle (the inferolateral border of the suboccipital triangle)
- The semispinalis capitis (The roof of the suboccipital triangle)[2]
Rectus Capitis Posterior Minor
- Origin: The tubercle of the posterior arch of the C1 vertebrae (atlas)
- Insertion: The inferior nuchal line of the occipital bone
- Action: Extension of the neck
Rectus Capitis Posterior Major - Superiormedial Border of the Suboccipital Triangle
- Origin: Spinous process of the C2 vertebrae (axis)
- Insertion: The inferior nuchal line of the occipital bone
- Action: Ipsilateral rotation and extension of the head
Obliquus Capitis Superior - Superiorlateral Border of the Suboccipital Triangle
- Origin: The lateral mass of the C1 vertebrae (atlas)
- Insertion: The lateral portion of the inferior nuchal line
- Action: Extension and ipsilateral flexion of the head
Obliquus Capitis Inferior - Inferiorlateral Border of the Suboccipital Triangle [9]
- Origin: Spinous process of the C2 vertebrae (axis)
- Insertion: The lateral mass of the C1 vertebrae (atlas)
- Action: Rotation of the head
Semispinalis Capitis - Roof of the suboccipital triangle [10]
- Origin: Articular processes of C5-C8 vertebrae and the transverse processes of T1-T6 vertebrae
- Insertion: Superior to the inferior nuchal line
- Action: Head extension
Surgical Considerations
The suboccipital nerve may suffer injury in surgeries involving the posterior neck at the levels of C1 and C2. Surgeries involving the midline suboccipital approach, such as distal vertebral artery bypass or access to the fourth ventricle of the brain, and posterior approaches for cervical neck fusions may damage the suboccipital nerve.[11]
Clinical Significance
The suboccipital nerve may play a role in the pathogenesis of cervicogenic headaches and occipital neuralgia. The nerve may also be vulnerable to trauma from whiplash injuries.
Occipital neuralgia, also called C2 neuralgia, is a condition of recurrent headaches localized to the occipital area of the head and neck. Occipital neuralgia is described as a sudden onset neuropathic pain generally unilateral in nature, but occasionally bilateral, across the dermatomes of the greater occipital nerve and the lesser occipital nerve.[12] The pathophysiology behind occipital neuralgia is thought to be due to irritation of the greater occipital nerve or lesser occipital nerve by external compression. Patients generally feel a brief shock, shooting, lightning-like, or stabbing-like pain distributed to the occipital nerve area. This pain can be brought on by pressure to the occipital area or by certain movements. For example, from excessively contracted muscles, cervical spondylosis, or fractures of cervical vertebrae. Due to the anatomic variations of the suboccipital nerve, it may play a role in the pathogenesis of occipital neuralgia, with some anatomic variants of the nerve attaching to the lesser and greater occipital nerves.[5]
Cervicogenic headaches present as a unilateral headache or migraine brought on by movement or palpation of the cervical vertebrae. The pain can present anywhere on the scalp due to the referred pain of nerves, but it primarily presents in the posterior area of the neck. The pathogenesis of cervicogenic headaches appears to be due to cervical vertebrae pathology affecting the C1-C3 nerves. The suboccipital nerve may contribute to cervicogenic headaches, especially in certain anatomic variants where it connects with the greater and lesser occipital nerves.[13][14][15][6] For occipital neuralgia and cervicogenic headaches, occipital nerve blocks may be therapeutic and often diagnostic of the conditions.[16][17] Suboccipital injections of steroids have been treatments used in the treatment of cluster headaches and post-dural puncture headaches after C-sections.[18][19]
Like other muscles, the suboccipital muscles can become strained, resulting in neck pain, spasms, or headaches. Additionally, the suboccipital muscles and the suboccipital nerve can incur damage from whiplash injuries from car accidents or other rapid deceleration injuries. The theory is that damage to the suboccipital nerve that occurs due to whiplash injuries may be due to injury of the rectus capitis posterior minor muscle.[20] The treatment of suboccipital muscle strains, like other muscle strains, are generally supportive and include posture correction, massage, stretching, NSAIDs, yoga, acupuncture, and physical therapy.[21][22][23]
(Click Image to Enlarge)
Suboccipital triangle, Multifidus, Thoracic vertebra, First and Second Rib, Semispinalis capitis, Longissimus capitis, Oblique Superior and Inferior, Rectus Posterior Minor
Contributed by Wikimedia Commons,"Medical gallery of Mikael Häggström 2014" (Public Domain)
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Suboccipital Nerve, Greater occipital nerve, Cutaneous branch suboccipital nerve, Lesser occipital nerve, Third occipital nerve
Illustration by Emma Gregory